Mobile IP is aimed at enabling a mobile terminal to communicate with a communication party without any change in its IP address when moving from a subnetwork to which the mobile terminal has been linked to another one. In the Mobile IP, a node that continually moves and changes the connected subnetwork is called “mobile terminal” (Mobile Node; abbreviated to MN), the subnetwork to which the mobile terminal was originally linked is called “home link” (Home Link; abbreviated to HL), a node that is present in the home link and takes charge during the absence of the mobile terminal is called “home agent” (Home Agent; abbreviated to HA), a subnetwork to which the mobile terminal is actually linked is called “foreign link” (Foreign Link; abbreviated to FL), a node that is present in the foreign link to look after the mobile terminal while the mobile terminal is in the foreign link is called “foreign agent” (Foreign Agent; abbreviated to FA), an address that is assigned for the mobile terminal in the foreign link is called “c/o address” (Care-Of Address; abbreviated to COA), and an address that is uniquely assigned for the mobile terminal independently of the connected subnetwork is called “home address”. Incidentally, the communication party (Correspondence Node; abbreviated to CN) of the mobile terminal includes fixed terminals as well as mobile terminals.
In a network based on the Mobile IP, IPv4 and IPv6, following processes are generally performed.
Set out below are processes according to the Mobile IP.
(1) In the case where the mobile terminal is in the home link
As with the case of ordinary TCP/IP, the mobile terminal communicates with a communication party in the ordinary way.
(2) In the case where the mobile terminal is not in the home link
The mobile terminal detects that it is somewhere other than the home link, and executes “Home Registration”, that is, notifies the home agent of a new c/o address through the foreign agent so that all packets to its home address are forwarded to the mobile terminal.
(2-1) The arrival of packets
The packets sent to the home address from the communication party arrive at the home link through the mechanism of normal IP routing. The home agent catches the packets by Proxy ARP or the like, and forwards the packets to the foreign agent in the network where the mobile terminal is present by tunneling. Thus, the mobile terminal receives the packets.
(2-2) The transmission of packets
When the mobile terminal transmits packets to the communication party, the header of each IP packet still contains the home address as a source address. In the case where any error occurs on the way, the packets are sent to the home address and, consequently, returns to the mobile terminal through the above-mentioned mechanism.
Incidentally, there has been promoted the standardization of the mobile communication system “IMT2000” for the mobile communication service providing more high-speed broadband access, and one of the main services is an offer of IP packet communications. The application of the Mobile IP is under review as a method for the location management of mobile terminals on the IMT2000 network.
FIG. 9 is a diagram showing the configuration of an IP packet network envisioned for the IMT2000 network. In FIG. 9, mobile terminals 1121 and 1122 each have an IP address (home address) assigned by the IP packet network of IMT2000 as a managing body, and set/manage a radio access link with a packet data support node (Packet Data Support Node: PDSN) 1106 or 1107 in the place where they have moved via radio base stations 1102 to 1105.
A packet data gateway node (Packet Data Gateway Node: PDGN) 1108 provides the home agent function of the Mobile IP as well as the function of a gateway router for connecting the IMT2000 packet network with an IP core network 1111 such as the Internet.
Each of the packet data support nodes 1106 and 1107 is situated with respect to each specified area in the IMT2000 packet network, and supports a certain number of the radio base stations 1102 to 1105. The packet data support nodes 1106 and 1107 set/manage radio access links with the mobile terminals 1121 and 1122 where they are connected via the radio base stations 1102 to 1105, and also provides the foreign agent function of the Mobile IP. In addition, the packet data support nodes 1106 and 1107 serve as default routers for packets transmitted from the mobile terminals 1121 and 1122.
In the IMT2000 network having this configuration, following processes are performed.
First, the mobile terminal 1121 sets a radio access link with the packet data support node 1106 uniquely designated with respect to each radio base station to send a Mobile IP registration request. Having received the Mobile IP registration request, the packet data support node 1106 forwards the request to the packet data gateway node 1108. When receiving the Mobile IP registration request, the packet data gateway node 1108 manages the association between the IP address of the mobile terminal 1121 and that of the packet data support node 1106 to which the terminal 1121 is currently connected, and returns a Mobile IP registration response to the packet data support node 1106. The packet data support node 1106 forwards the received mobile IP registration response to the mobile terminal 1121, and manages the association between the IP address of the mobile terminal 1121 and the link ID of the radio access link.
The packet data gateway node 1108 catches all IP packets transmitted from a communication party 1112 connected to the IP core network 1111 to the mobile terminal 1121, and forwards the packets to the packet data support node 1106 that serves as the foreign agent of the mobile terminal 1121 by IP tunneling. The packet data support node 1106 reconstructs the IP packets which have undergone the IP tunneling, and forwards the packets to the mobile terminal 1121 via the radio access link with the associative link ID. On the other hand, the packet data support node 1106 performs routing according to their destination and forwards IP packets transmitted from the mobile terminal 1121 to the communication party 1112. Besides, IP packets transmitted from the mobile terminal 1121 to the other mobile terminal 1122 are routed from the packet data support node 1106 that serves as the foreign agent of the mobile terminal 1121 in the transmitting end to the packet data gateway node 1108. The packet data gateway node 1108 forwards the IP packets to the packet data support node 1107 that serves as the foreign agent of the mobile terminal 1122 in the receiving end by IP tunneling. Accordingly, the mobile terminal 1122 receives the IP packets.
Examples of the network protocol for handling the mobile terminals include Mobile IPv4 and Mobile IPv6. However, since the mobile terminals and IPv6 mechanism assume the role of the foreign agent, the foreign agent does not exist in the Mobile IPv6.
Set out below are processes according to the Mobile IPv4 and IPv6.
(1) In the case where the mobile terminal is in the home link
As with the case of ordinary TCP/IP, the mobile terminal communicates with a communication party in the ordinary way.
(When adopting the IPv6, the mobile terminal sends a registration request directly to the home agent.)
(2-1) The arrival of packets
In the IPv6, the mobile terminal that has received packets forwarded by tunneling transmits a new registration request to the communication party that sent the packets, and notifies the communication party of the c/o address. After that, the communication party transmits packets directly to the mobile terminal on the basis of the c/o address.
(2-2) The transmission of packets
When adopting the IPv6, the c/o address is set as the source address, and the home address is indicated as a newly defined Destination option.